Selective gearing arrangement for hobbing gears and milling threads



June 22, 1965 J. A. BRADN ER SELECTIVE GEARING ARRANGEMENT FOR HOBBINGGEARS AND MILLING THREADS 2 Sheets-Sheet 1 Filed Nov. 14, 1963 illlilH I5 [Em ullllumum \lllllllllllillllllll "ll 4 lllllllllli llllllllHllllilllh INVEN TOR. Joan Q. Banana.

June 22, 1965 J BRADNER, 3,190,180

SELECTIVE GEARING ARRANGEMENT FOR HOBBING GEARS AND MILLING THREADSFiled Nov. 14, 1965 2 Sheets-Sheet 2' 1 I llllllllllllllll lllh 1|||||||w l I 1 l I 101 5- 95 1 i 21b 1 Hill y 2.9 1 L05 II ':A, 7 El 7' if kLOG 2 v 03 E3 :lllllllllll ||||||||||li IEEE L02 (,9 70 L04 3 INVENTOR.Jam A. Bummer.

@WKM M United States Patent Ohio v Filed Nov. 14, 1963, Ser. No. 323,832

4 Claims. (Cl. 90-4) This invention relates to machine tools and moreparticularly to a gearing system which may be selectively utilized inand forming a part of a single machine capable of performing a pluralityof basically dissimilar machining operations on selected workpieces,such, for instance,

as gear and spline hobbing operations and thread milling operations,where the maintenance of a proper timed re iationship between therotation of the lead screw driven by suitable lead gearing, and themovement of the workpiece, is essential.

The two arts of hobbing and thread milling are well known and thoseskilled in these arts are familiar with means developed to hob gears andsplines in the one art and, in the other art, other means tomillthreads, as represented by US. Letters Patent 2,563,982, HobbingMachine, and US. Letters Patent 1,156,237, Thread Mill ing Machine,respectively. 7

It has been recognized in the past that very real econo mies wouldresult if a single machine could bedevised which would be capable ofboth bobbing gears and splines and of milling threads. Attempts in thepast tocombine these two techniques have failed, primarily for tworeasons, the first being the fact that previous'hobbing machines, whenput to work thread milling, would lose lead relationship establishedduring a first or trial'cut, after quick returning,precluding'satisfactory gauging to establish size, and resultinginexcessive scrapping of specially prepared components, whereas threadmilling machines, when put to work hobbing gears or splines, thoughcapable of bobbing, again lose helical gear lead relationship after acut and during quick Ieturmagain precluding the possibility of gaugingand the taking of subsequent cuts to establish size.

In addition, in the art of bobbing, the rotation of the cutter or hobmust be synchronized exactly with the rotationof the workpiece whereas,in the art of'thread milling, it has been recognized that means must beprovided whereby the speed of rotation of the cutter and the speed ofrotation of the workpiece can vary independently.

For example, the thread milling machine disclosed in US. Patent No.1,156,237 did not possess these inde-' pendent drive means, afailing'that was discoveredand corrected in the later thread millingmachine, US. Patent No. 2,405,522, wherein the common backshaft drive ofthe earlier thread milling machine was replaced by a dual motor drive inthe latter tool, one motor "and varia ble speed drive means was providedto operate'the thread millers cutter head, and a second independentmotor and its variable speed drive mechanism was provided to operate thethread millers workhead.

This second Workhead drive means in a thread miller must be capable oftwo separate functions, first, slow rotation rates for feed purposes,whereby the required relative axial feed motion between the workpieceand thread milling cutter will be produced so that threaded sections ofthe required lead or pitch will be generated by feeding the workpiecepast the cutter or feeding the cutter past the workpiece in proper timedlead relationship. It will immediately be apparent to those skilled inthe art that although the relative axial motions of the workpiece andcutter parallel to the axis of the workpiece must be synchronizedprecisely tov generate threaded sections of the requiredpitch or leadthe relative rates of 3,190,184 Patented June 22, 1965 actual rotationof the workpiece feedingandthe cutter, milling, are completelyindependent of each other,.the precise converse of the conditionsprevailing when gears are being bobbed.

The other function that the workhead drive mechanism of the threadmiller must create is that of quick return without losing timedrelationship established during the first cut, for gauging purposes andthe establishment of the desired final depth of cut to the size desired.

It will be observed on further study of these two last mentioned patentsthat what is achieved in the normal thread milling machine workhead isfeed means through a feed clutch, reduction gearing, and suitable feedgearsired lead or pitch of the threaded section to be produced 7 will begenerated, and a manually operable rapid traverse means, whereby onmanual disengagement of the feed clutch and subsequent manual engagementthereafter of the rapid traverse friction clutch, the entire workheadmechanism comprising the feed gearing, the work spindle and workpiece,the lead gearing and thence the lead screw will be caused to spin at avery much higher rate, in asense or direction opposite to the directionof the feed, achieving rapid return.

Upon review of this functioning it will be further observedthat, by wayof these two means, the relationship between the cutter and the threadedsection generated during the first cut is maintained and is not lostduring rapid return,;thereby enabling the necessary gauging or measuringand the taking of a second or more cuts till the desired size or depthof threaded section to be produced is achieved.

To those skilled in the art, it will immediately be ap parent that, inthe case of a thread milling machine such as the mechanism disclosed inUS. Patent No. 1,156,237, because of the fact that this is a threadmilling machine in which the cutter head and the workhead are powered bya common source, the backshaft, that thereby the cutter and the workmight, if desired, be caused to rotate in the proper timed relationshipby the proper choice of feed gears and lead gears, thereby enabling theuse of this thread miller for the hobbing of gears by the usage of thisproperly selected gearing and the substitution of a suitable hobreplacing the normal thread milling cutter with which the thread millerwould normally be arranged. However, to those skilled in the art, itwill immediately be apparent that two factors mitigate against thesatisfactory usage of a thread miller such as this if gears are to behobbed. In the first place-the gearing calculations, ifgears are t'o'behobbed, are extremely cumbersome and laborious, and secondly, ifhelicalgears are to be produced, although the thread miller willmaintain lead when operated as a thread miller, lead relationshipbetween the hob and the gear when hobbing is not maintained but is lostif an attempt is made to employ the thread miller as a helical gearbobbing machine, precluding the possibility of gauging when size isbeing established when either the machine is first being set up or whenchanging cutters, i.e., hobsJ In a review of the hobbing process and thekinematics that enable the required timed rotation of the hob and theworkpiece, the gear blank, the required relative feeding motion, and inthe case of a helical gear, the addition of the required supplementaryelement of angular rotation of the workpiece in timed relationship withthe IQ- tation of the lead orfeed screws, to create the desired elementto create the desired amount of skewor amount of skew or helical advanceof the workpiece, the

helical gear being produced, it will be observed in the case ofa hobbingmachine, such as the mechanism described in Patent No. 2,563,982, thereare certain basic elements required to achieve. the necessaryrelationships. Whereas in thecase of the thread milling machinesWorkhead, it will. be recalled there was required a pair of clutches toimpart a relatively lower rate of operation or rotation of the workheadmechanisrn to achieve a suit able feeding rate and alternatively arelatively very much higher. rate for rapid return, suitable feedgearing, means to drive the workpiece, the Work spindle, and finallysuitable lead gearing in correct association with the'thread' millerslead screw to generate the desired pitch or lead of the component tobethreaded, the screw thereby caused to rotate in proper, timedrelationship with-the work spindle, i.e. the workpiece,.the kinematicsof the hobbing machine, e.g. PatentNo. 2,563,982, seem to vary markedly.I

. In the art of generating toothed sections bing process, unlike 'thethread milling art, the cutter (the hob) must be rotated in precisetimed relationship with the rotation of the workpiece, and, in the caseof via the hobposes to establishproper size, it will be noted bothin thegeneration of helicalsections, not only 'must: the

rotation of the hob'be in precise timedrelationship with the'rotation ofthe workpiece but, in addition, for the creation of the helical advanceor skew of the component being generated, there must also be asupplementary equally precise .timed relation between the supplementaryangular advance of the workpiece and the rotation of the skew. t a H To.those skilled in the art, the kinematics of the gear hobbingmachine,.e.g. Patent No. 2,563,982, are well known. Power to drivethemachine is supplied from some fixed or variable mechanism such asamotor driving a common backshaft, causing the cutting tool, i.e.. thehob, to rotate at a suitable cutting speed. Said backshaft also drivesthe Workhead 'of the hobbing machine. In the case of a dualdifferentialmechanism, suchas is disclosed in U.S.-Patent No. 2,563,982,said drive is brought through .theinternal components of the leadditferentialjmechanism, differential L, to suitable index change gearsA/B/ C of the required ratio to cause the work spindle and the workpieceto rotate at the proper timed rotation rate .with the hobbing spindleand hob that the required number of teeth will be.,generated by thecutting tool or hob.

Said rotation of the-work spindle canalso be employed to cause the leadscrew of the machine to rotate at a proper feeding rate via the choiceand selectionofsuitmechanical brake) to the lead screw. To those skilledin the art, the wisdom of thisseries type of dual dilferentialinstallation will be immediately apparent.

And tothose skilled in the artyit will also be immediately apparent thatthis means ,of drive to the traverse screw of the hobbing machine, thelead screw, can also" ciation therewith via suitable gearing means,rapid traverse or quick? return of the mechanism to the starting pointthe case of spur gears, when the lead ditferentialrnechanism is lockedout of engagement and is inoperative, as

wellasin the case of the generation of helical gearing,

when thelead differential. mechanism is employed and is operative, thatthe relationship between the :cutting tool, the hob,'and the workpiececreated the initial cut is not lost and is maintained during andafterthe rapid traversing, bydilferential L, thereby enabling readymeasuring or gauging of the. workpiece and a second or J more cuts to.be taken to enable' the .milling of threads, 'for'if lead: difierential1 mechanisms 'case 22'is locked and-if lead change gears G/H J areremoved and renderedinoperable, if what now suitable threading leadchange .D/E/F gears are substituted .for what were the feed gears in thecase of the use i of the machine as a gear hobber, it will be observedthat. the work spindle and hence the workpieceand thence the:

lead screw can be made to rotatein the proper timed relationship so thatthere will transpire the properly'timed relative feeding motion betweena thread milling cutter,

substituted for the normal gear hob, and the workpiece. so that threadsof the desired. lead or ditierential T is nowspu'n atsome suitablerate-via a separate means, such as a rapid traverse motor in assocan andwill be achieved. However, it will immediately be apparent that the sameproblem, employing theconventional hobbing machine as athread miller aswell,

occurs when rapidtraversing that transpired'wh'en a classic threadmilling machine was used as gear hobbing machine.

The lead relationship, established during the initial cut possibility ofgaugingfthe component and then taking a subsequent. cut or cuts to to.the desired size.

It will be observed that, whereas in the case of the con-. ventionalgearhobbing machine, the workpiece and the. cutter or hob must berotated'in the precise timed relationship, when the thread millingproces is employed, vit

and the thread millers' cutter, spindle, independently'of each other.Hence, when an endeavor is made to produce be employed as a means ofespecially satisfactory moment to obtain the required supplementaryelement of angular displacement of-the workpiece to create helical orskewed workpiece sections, for in the case-of reductions to practicesuch as Patent No; 2,563,982, the rotation of the machines lead screwdrive mechanism can thereof.

, On completion of the cutting or bobbing operation, to

obtain rapid return to the starting point for gauging pur helix threadsvia the milling process'on the conventional hobbing machine, means are*not at hand to. vary either the work spindle or the cutter spindle,speedsindependently.

Finally, another reason thatspreviously. est'oppedthe.

usage of one machine for both gear hobbing andfthread milling'as well isthefact that apparently work spindle rotation rates for the, twoprocesses are so different that.

unless extremely costly and complex reduction gear-boxes are resorted tothat the differences of rotation ratesrare incapable of resolution,In'the case of bobbing, for example, work spindle rotation rates arerelativelyhigh;

if a twenty tooth gear or spline is being generated with a single starthob operating at a speed of 400 r.p.m., the work spindle must be rotatedat 20 rpm. V.

. On the other hand, if, for example, a 4" diameter one inch lead wormis being milled using a feed rate of. three pitch can and will bring thepart being threaded inches per minute, the thread-milling machine mustbe spindle will make but one revolution in about four minutes, or thatit will operate at a rate of /2%. r.p,m. Although it is true that thesewidely variant rates can be combined, the'means to so do are excessivelycostly and complex, another reason that in the past efiorts to comblue,in but one meachine, means to hob gears and splines and to mill threadsas well, have not succeeded.

My invention solves these problems in an inexpensive, extremely simplemanner, enabling the satisfactory combining, in but one machine, ofmeans to hob spur and helical gears orsplines, maintain relationshipduring quick return for gauging and sizing purposes, mill threads orworm sections on the same machine, at the proper work and cutterrotation rates, and maintain lead relationship during quick return forgauging purposes and the taking of a second or more cuts, via a new andnovel employment of what is normally the lead differential on a hobbiugmachine, serving also as a rapid traverse differential mechanism withits own separate rapid traverse drive mechanism for thread milling rapidtraverse, in association with a new and novel method of shifting ormoving the drive shaft on which there are male splines, into or out ofengagement with female splines in driven members toenable selectiveclutching or declutching thereby without resorting to the usual expenseand complexities of conventional positive jaw clutches.

It is an object of my invention to achieve the setting up of thetransmission mechanismin a machine tool of the type for hobbing gears,helical gears and splines, whereby said mechanism may readily and easilybeconverted to operate the machine as a thread miller, and vice versa.

A further object of this invention is a single machine tool mechanismselectively operable to utilize the machine for gear and spline hobbingor for milling threads.

Another object is a single machine tool selectively capable of threadmilling and/ or hobbing gears and splines by utilizing simple selectivemeans forming a part of the transmissionmechanism for establishing a.proper timed relationship between the cutter and work spindles withoutmaterial changes, in the common power. transmission mechanism, thuseliminating the necessity for time consuming and tedious calculationsfor such translations of the mechanism and further without destroyingthe, accuracy of the work produced by the machine in either instance.

Another object is to provide a machine of the type disclosed in which isincorporated novel means by which the machineslead differentialmechanism, when hobbing, can be utilized as the machines rapid traversedilferential mechanism when threading and also enables the usage of whatis normally the machines rapid traverse dilferential mechanism, whenhobbing, as a longitudinal positioning device to reestablish therelationship of a thread already cut that has to be recut, to thecutter.

A. still further object is to economize in the production of hobbcdgears and splines and the like, as well as in the milling of threads bythe elimination of separate and independent machines for theserespective operations, with the attendant set-up in each instance,while, at the same time insuring accuracy of the. finished pieceproduced by these operations in a singlemachine.

Another object is to provide means whereby the speeds or rates ofrotation of the work spindle and the cutter spindle may be varied orselected independently.

Other objects and advantages of this invention will become more apparentas the following description of an embodiment thereof progresses,ireference being made to the accompanying drawing in which likereference characters are employed to designate like parts throughout thesame.

In the drawing:

FIGURE 1 is a diagrammatic view of a form of kinematics illustrating howthe same may be employed in a 6 single or multiple station gear andspline hobbing machine; 1

FIGURE 2 is a view similar to that of FIGURE 1 and illustrates how thestructure of FIGURE 1 may be utilized for thread milling; and

FIGURE 3 is a schematic perspective view of a portion of thedifferential mechanism shown in FIGURES 1 and 2.

In carrying out my invention, I have illustrated a form thereof in theaccompanying drawings from which and from the following description, itwill readily be seen that the gearing system basically may be utilizedin a single machine under certain conditions and with certain gearingarrangements easily effected by the operator, i.e., the selectiveapplication of motive power to utilize the lead differential mechanism,when hobbing, as the machines rapid traverse differential mechanism,when threading, and to employ the machines normal rapid traversedifferential mechanism, when hobbing, as a. longitudinal positioningmeans to re-establish the relationship of a thread already cut, and thathas to be recut, to the cutter.

Referring first to FIGURE 1, which illustrates the invention in use for,performing a gear or spline hobbing op eration on a workpiece as, forinstance, is fully disclosed in my copending application entitled: MainDrive Means for a Gear Hobbing 'Ma'chine, Serial No. 252,656, filedJanuary 21, 1963, the hob 18 is driven by a source of power such as ahydraulic motor 6 through the method gears 15 and 1 6. The motor 6 hassuitable connection with a fluid pressure source as the pump 3 driven bymotor 4. It is preferred that the motor 6 be carrieddirectly on theswiveling portion of the hob head of the machine and delivers its powersubstantially directlyto the hob spindle through the gears 15 and 16 andsecondarily by means of the shaft 13 through the bevel gears 22 and 23,the sliding spline connection 24 without disrupting the drive during anyswivel action 'of the hob head, thence through shaft 24, bevel gears 25and 26 and sliding spline connection 21- to the main drive shaft or backshaft 21 and through a sliding spline connection 21 on'the lower.

end of the back shaft to the bevel gear27; With the parts in theposition shown, power from the drive shaft 21 is transmitted through thegears 27, 28 to shaft 29 and through the meshed gears 30- 31 to thediiferential input shaft 33, or the gears 30, 31 may be eliminated andshafts 29 and 33 may be a single shaft.

Differential mechanisms, indicated generally at L and T includerotatable frames 34 and 35, respectively, and input shafts 33* and 36,respectively. In FIGURE 3 I have illustrated in diagrammatic form theinternal gearing of the differentials L and T, the rotatable coverhaving been removed in this figure. A gear 37 is secured on inputshaft33 and spaced from and axially aligned with it is a gear 380m theoutput shaft 39. Intermeshing differential pinion gears 40 and 41 arealso respectively meshed with the gears 37 and 38. Rotatably supportedpinion shafts, indicated at 42 and 43, respectively, are supported inthe rotatable frame 34.

The mounting of the differential spindles 42 and 43 on the differentialframe 34 is relied upon to communicate the increment of speed variationto be imparted to the gear 38 and the output shaft 39 by the effect ofrotation of the worm wheel 32. by motion derived from a shaft 44, sincethe rotational rate of the gear 38 is at arate which is the algebraicsum of the rotational rate of the input gear 37 plus the rotational rateimparted by the worm 45 to the frame 34.

This action is similar with respect to the acceleration of rate ofrotation imparted to the shaft 44 carrying the gear 46 by rotation oftheframe 35 of the dilferential mechanism T by the driving effect of theworm 47 on the gear 48. a

A set or group of index gears may be variously arranged, but, asillustrated in FIGURE 1, may comprise a driving index gear 4-9 securedtothe differential output 7 a shaft 39 anda driven output gear '50:secured to the shaft 52, there beingrone or more intermediate indexgears-'51 interposed between and inserial relationwith the gears 49 and50.. To the opposite end of the shaft 52 is secured a worm pinion 53 andthe worm wheel 54 is rigidly fixed to the work spindle 55 whereby thelatter is rotated at a precise or exact rotational rate by theworm'pinion 53.

' rispeed;regardless of anyiconcurrent 'rotary movement im parted to thedilferentialgear 62 'by the feed geari61'.:

A helical gear 56 afiixed to the work spindle drives a relatively matinghelical gear 57 fixed to the shaft 58 when the spindle is rotated. Fixedto the opposite end of the shaft 5 8 is a driving feed gear 59 which isin mesh with one or more intermediate gears 60 for transmitting drivingmotion to the output feed gear 61 carried on the outer end.

of shaft 36. Theshaft 36 carrieson its inner end,*which is disposedwithin, the rapid traverse differential casing 35,"

' 44 in longitudinally spaced relation and rotational movementimparted'to the shaft 44 and communicated to the worm pinion 64 causes thispinion to drive the Worm gear;

65 which is rigidly fixed to the lower end of the lead screw 66, wherebyrotary movement is given to vertically move the hob carriage to causethe required feed movement of the hob-spindle while moving transverselyacross the periphery'of arwork blank placed 'onthe work spindle 55, andin a'direc'tion parallel to the axis of the Work' spindle. i V pRotational movement imparted .to the shaft44 will,

through the meshing bevel gears 63 and 67, drive the lead gear 69affixed to the opposite end of the shaft 68. A-v

second lead gear 70 is carried on the adjacent end of the shaft 72 andis driven by means'of an intermediate gear 71 in'mesh with the gears 69and 70, and as a result of rotational movement ofthe shaft68y Rotationalmove-.

ment of the lead gear 70 is transmitted through the shaft 7 '72 andthrough a set of relatively intermeshed gears 73, 74 and 75, gear 73being fixed to' the upper endiof shaft 72 and gear 75 being fixed to theupper end of shaft 76. To the oppoiste end of shaft 76 is fixed theworm'45 which is intermeshed with the worm wheel 32 fixed to the hub 32of'the rotatable lead differential frame 34.

At 77 I- have illustrated a rapid traverse motor which has a doubleended shaft 78 to which at one end a brake drum 79 is affixed anddisposed in operative relation to brake shoe devices of a well knowntype, with automatic means adapted to retract the brake shoes torelease-the which, being meshed with a bevel gear 81 fixed to shaft 82;

will drive the worm wheel 48 through the worm pinion 47 fixed to theshaft 82' and which is' in mesh with the' worm wheel 48, the wormwheel48 being carried by the hub 83 fixed to the rotatable frame 35 ofthe rapid traverse I driving effect of the relatively rapid rotatingworm 47 on the worm gear 48, whereby to effect added rotational 111FIGURE 2, I have illustrated substantially the same gearing'and drivelayout as that shown intFIGURE' 1 and described above and'have;,inaddition, illustrated r leans by which this mechanismand layout mayreadily and quickly be converted into a machine for milling threadswithout substantial change in the arrangement to thereby accomplish thefull ,utility'of the machine. for both bobbing and threadmilling'operations. 'Ihe necesi sity for additionalfloor space andadditional expensive separate machines in orderto carry out'theseseparate,

operations is alsoeliminated.

According to the present invention, when'a hobbing machine suchas thatdisclosed in Patent No. 2,563,982,I equipped with a lead differentialmechanism shown at L K in thepresent disclosure, is to beemployed as athread milling machine, the lead differential drive shaft76 iisextended'as at'76 and this extension carries a driven sheave 'keyed,thereto and suitably connected by V belts 91 to a threading frapidtraverse drive. motor which, in turn, is operatively connected tothreading 1 rapid traverse motor brake 93 so arranged'in the normalthreading operation that,' when the motor is energized,

the brakes solenoid (not shown) is also engaged 'releasa ingthe brakeshoes 94 and loosening the brake; de-

energizing the motor alsofde-energizcs the brakes sole-, r noid to setthe brake and to thereby quickly and acc'urate- When thread milling thevidler gear 71 is, of course, disengaged from the bobbing machineslead'gear train, disconnecting and permitting ly stop the rapidtraverse;

the shaft 63 to run freely. r r

"As shown and described hereinbefore, when theme;

chine is operating as a hobbing machine, power to "drive a the hob 18and the work spindle 55 carrying a blank or. workpiece (not shown),causing them to rotate in proper timed relationship, istran smitted froma fixed or variable speed power source, such as the hydraulicmotor 6,di: rectly to the hob head and hob and to the drive or back shaft 21simultaneously, through the permanently splined coupling 21* and throughthe engaged splined coupling members 21 drive bevel gears 27 and 28,shaft 29, gears 33 and 31, shaft 33, lead differential L and through thegear train 49', 51, 50, 52, 53 and 54 to the work head 55; a

It will be observed thatthe back shaft is, in addition to its'rotativemovement and by virtue of the permanent sliding spline couplinglat 2 ltand the slidingly separable spline coupling at 21*, also capableof-axial movement,

to axially'engage and disengage the telescoping male and female splinemembers 21' carried on the shaft 21 and bevel gear 27, respectively. 'Inorder to axially shift this shaft 21 into and out of driving connectionwith the power sources 6 andlllZ, respectively, any suitable means maybe provided: c When the shaft 21 isin the position shown in FIGURE 1'(for bobbing), the spline members 21 are engaged as are the splinemembers 21,-

but when shaft 21 is shifted axially upwardly as in FIG- URE 2' (forthread milling), the driving connection.

throughthe spline member ZIP is broken by disengaging these members. Oneform of such shift means is'shown diagrammatically as including agrooved collar 95: fixed. on the shaft 21 to rotate'therewith, a shiftlever, 96 m1 crumed at 97 to a supporting base 98 and having an operfating handle or arm 99 at one end while its opposite enddirectly driveshaft29'through the belts 1031 and sheaves 104 and105, the. latter beingkeyed to the extended end 106 of the drive shaft 29. This arrangementpermits rotation of the work head of the machine at the relatively lowerrates of work spindle rotation for thread milling purposes.

Under these conditions, the variable speed drive source 6 can beemployed to vary, at will, the cutter spindle speeds when threadingwithout effecting work spindle rotation speeds when threading, since thepower sources 6 and 102 are separate and independently controlled forpowering the work head for feed.

' It will be observed now that what had served as index gears 49, 50 and51, when hobbiug, become the gears that control work spindle rotationrates when threading, that is, the threading feed gears. Likewise, gears59, 60 and 61, which had served as feed gears when hobbing, now become,through the choice of proper ratios, the machines feed gears, whenthreading. For instance, if the ratio of the gear 56 to the gear 57 is aratio of three to two and the ratio of the worm and wheel 64 and 65,respectively, is two to fifteen, and the pitch or lead of the lead screw66 is, in this instance, a lead of one-half inch, the overall lead ratiobecomes 3:2 x /z or 1: 10. It will be seen that this produces a verysatisfactory and easy calculation for threading since the (threading)lead gears now become merely the lead to be milled times ten.

Thus, when the well known kinematics of the hobbing machine areregrouped, according to this invention and by the means disclosedherein, it will be understood that the required low rate of work headrotation for feed, when threading, is now most satisfactorily obtainedby disengaging the back shaft drive from the gear 28 through the spline21 operatively connecting the work head drive motor 192, and that forthreading rapid, by selectively operating threading rapid motor 92, andrapidly rotating differential frame or case 34, the work head can bespun at a desired higher rate essential for rapid traverseat the sametime maintaining the required relationship between a threading cutterand work piece established during a first trial cut for subsequentgauging or measuring and thereafter additional cuts to bring the piecebeing threaded, to the desired size. Thus the lead differentialgenerally shown at L, when hobbing, can be employed as the same machinesrapid traverse difierential when threading, enabling the maintenance ofthreading relationship between the cutter and the piece during and afterrapid traverse. When threading, the differential T (rapid traversedifferential in hobbing) is not used in that operation of the machine.However, a piece once threaded and then removed from the machine andwhich may have to be re-cut for any reason, the differential T can nowcarry out a new and extremely vital fimction when the machine is beingemployed as a thread miller. Ordinarily, to pick up accurately a sectionof a piece that has been threaded with a threading cutter is anextremelylaborious and time consuming operation, but by my invention, I utilizethe hobbing machine kinematics in a novel manner whereby the hobbingmachines lead differential mechanism in hobbing becomes the machinesrapid traverse differential mechanism, when threading, and furtherenables the use of the machines rapid traverse differential mechanism T,when bobbing, as a longitudinal positioning means to reestablish theproper relationship between a thread already cut, and that has to bere-cut, and the cutter.

Shaft 78 is extended to terminate in a hand wheel 107, which is utilizedto rotate the shaft and, through gears 80 and 81, to rotate the worm 47causing worm wheel 48 affixed to the differential frame or case 35 toturn, thus locking the gears 59, 60 and 61 from'turning due to thelocking action of worm 53 and worm wheel 54. Under these conditions,rotation of the differential case 35 will cause the output drive shaft44 and lead screw 66 to turn whereby exact manual positioning of thecutter 18 with relation to a part that has been threaded, removed fromthe machine, and that has to be re-established in the machine forre-threading, can be easily and quickly carried cutter to the alreadythreaded section.

The selective conversion and operation of the machine as a hobbingmachine or as a thread milling machine is easily and quicklyaccomplished.

The machine, in bobbing, as illustrated diagrammatically in FIGURE 1, ispowered by the hydraulic motor 6, while the motors 102 and 2 which drivethe shafts 29 and 76, respectively, are inactivated by disconnecting thedrive belts 103 and 91 from the respective motor sheaves, thusfurnishing power directly to the hob 18 and through the permanentlysplined' connection 21 to the drive or back shaft 21, and through theengaged spline members 21 and gears 27 and 28 to the shaft 29 to drivethe lead differential, indexing and feed gears, the work spindle, therapid traverse differential and lead screw, rapid traverse beingelfected'by operation of the motor brake 79.

In FIGURE 2, the same machine is illustrated as converted for use as athread miller simply by replacing the hob 18 with a milling cutter 18'and disengaging the back shaft spline members 21 which is accomplishedby axially sliding the back shaft upwardly on the permanent spline 21through movement of the lever and handle about its fulcrum 96, from theposition shown in FIG- URE 1 to the position shown in FIGURE 2,sufliciently to etfectdisengagement of the spline member 21 A directdrive to the shaft 29 is effected from the motor 102 by assembling thebelts on the sheaves 104 and 105. It is also necessary to disengageeither gear 71 or gear 74 by any suitable means from the respective geartrains 69, 70, 71 or 73, 74, 75 and to establish a direct drive to theshaft 76' and worm 45 from the motor 92 by replacing the belts 91 on thesheaves 90. The hand wheel 107 is employed, as explained above, torotate the shaft 78 causing worm wheel 48 to turn and eifect a lock inone direction between the worm47 and the worm wheel 48 causing outputdrive shaft 44 and lead screw 66 to turn to exactly and manuallyposition the cutter with relation to a threaded part re-established inthe machine for re-threading.

From the foregoing, it will be seen that by effecting a few simplemodifications in the well known general kinematics of a hobbing machine,such a machine can readily and easily be converted to a threaded miller,or vice versa, thus conserving floor space, but more important,affording dual precision operations in a single basic machine. Whilesuch results have long been desired and sought after by those skilled inthe art, they have not been accomplished heretofore to my knowledge.Furthermore, I have produced the desired result by employing a uniqueand relatively simple conversion means enabling a single machine tofunction selectively for performing a hobbing operation on a piece orfor performing a thread milling operation while retaining the fullcharacteristics of the selected operation.

I claim:

1. A machine tool selectively convertible for use as a hobbing machineand for thread milling comprising a tool spindle for receiving aseiected cutter thereon, a main drive shaft, a single drive means forthe spindle and drive shaft, a rotatable housing lead diiferentialmechanism, a first index gear train, a work spindle, a rotatable housingtraverse differential mechanism, a lead screw, said drive shaft having areleasable drive connection with the input to said lead differential, asecond index gear train driven by said single drive and having a driveinput to the traverse differential, said first index gear traindelivering the output of said lead differential to the work spindle torotate the same at a precise rotational rate, said second gear traindetermining the cutting gear rate of a tool on the tool shaft, means fordisengaging the drive shaft drive to the work spindle, a selectivelyopen and closed gear train having driving connection only, when closed,with said lead screw and with the rotational housing of the leaddifferential mechanism, a prime mover energizable for effectinga preciserotational rate the workspindle through said 'lead differential andindependent from said drive shaft when the releasable drive connectionofthe drive shaft 1s disengageiand a second prime mover energizable foreffecting a driving connection with the rotational housing of the leaddifferential when the selectively open and closed gear, train is open,whereby respectively the selected relationship of the rotational rateofthe work spindle to the tool feed rate isirnaintained constant duringdis-engagement of the first and second prime movers while maintaming adriving connection between the drive shaft and the lead differential andduring maintenance of a closed drive of the gear train connectingthe'rotatable housing of the lead differential with the lead screw asinmilling.

2. A machinetoolselectively convertible for use as a hobbing machine andfor thread milling comprising atool spindle for receiving a selectedcutter thereon, a main drive shaft, a single drive means for thespindleand drive traverse differential mechanism, a lead screw, .said driveshaft having a releasable drive connection with the input to said leaddifferential, a second index gear train driven by said single drive andhaving a'drive input to the traverse differential, said first index geartraindelivering the output of said lead differential to the work spindleto rotate the same at aprecise rotational'rate, said second gear traindetermining the cutting gear rate of a tool on the tool shaft, means fordisengaging the drive shaft drive to the work spindle, a selectivelyopen and closed gear train 7 having driving connection only, whenclosed; with said lead screw and with-the rotational housing of the leadto the work spindle, a selectively open and closed geartrain havingdriving connection only, when closed, with said lead screw and with therotational housing of thelead differential mechanism, a prime moverenergizableforeffecting a' precise rotational rate'to the work spindlethrough said lead differential and independent from said back shaft whenthe releasable drive connection of the back shaft is disengaged, and asecond prime moverenergizable for effecting a driving connection withthe 'rotational housing of the lead difierential Whentheselectively openand closed geartrain is open, whereby respectively 7 g milling.

shaft, a rotatable housing lead differential mechamsmya Q first indexgear train, a Workspindle, arotat'able housing differential mechanism, aprime 'mover energizable for the rotational rate of the work spindle tothe tool feed rate is maintained constant during dis-engagement of'thefirst and scond prime movers while maintaining a driving connectionbetween the drive shaft and the lead differential and during maintenanceof a closed drive of the gear train connecting the rotatable housing ofthe lead differential with the lead screw as in performing a'hobbingoperation; and whereby the selected relationship between the rotationalrate of the work spindle to the tool feed rate may be maintained as inthread milling. t

3. A machine tool selectively convertible for use as a bobbing machine,and for thread milling comprising a toolv spindle for receiving aselected cutter thereon, aback shaft, a single drive means for thespindle and back shaft, a rotatable housing lead differential mechanism,a first index gear train, a work spindle, a rotatable housing traversedifferential mechanism,a lead'screw, said back shaft having at one end asplined connection with said single drive means and at its opposite endwith the input to said lead differential, and means for axially movingsaid back shaft into and out of driving connection with'said leaddifferential input, a second index gear traindriven by said single driveand having a drive input to the traverse V differential, said firstindex gear train delivering the output of said lead differential to theWork spindle to rotate the same at a precise rotational rate, saidsecond gear train determining the cutting gear rate of a tool on thetool shaft, means for disengaging the back shaft drive the selectedrelationship of the rotational rate of the work spindle to the tool feedrate is maintained constantcduringdis-engagement of the first and secondprimemovers while maintaining a driving connection between the backshaft and the lead differential and during maintenance of a closed driveof the gear train connecting the rotatable housing of the leaddifferentialwith the lead screw as in -performing a bobbing operation,and whereby the selected relationship between the rotational rate of thework spindle to thegtool feedrate may be maintained as in thread '4.'Amachinetool-'select'vely convertible for use as a hobbing machine andfor thread milling comprising a tool spindle for'receiving a selectedcutter thereon, a back ing at one end a splined connection with saidsingledrive means and at its opposite end with the input to said leaddifferential, and means for axially moving said back shaft into and outof driving connection with said lead differential input, said backshaft'axial moving means including a member'lixed to said back shaft forrotation therewith and a' second member carried by and engageable with,the

first me'mber and operable to impart axial movementto the rotatable backshaft to engage and disengage the back shaft drive connection with thelead differential input, a

second index gear train driven by said single drive and having a driveinput to thetraverse differential, said first index gear traindelivering the output of said lead differ.- ential'to the work spindleto rotate the same at a precise rotational rate, said second gear traindetermining the cutting gear rate of a tool on the tool shaft, means forare, engaging the back shaft drive to the Work spindle, a'seile'ctivelyopen and closed gear train ha ving driving connection only, whenclosed,'with said lead screw and with the rotational housing of the leaddifferential mechan-t ism, a'prime mover energizable for effecting aprecise rotational rate to the Work spindle; through said leaddiffer-'ential and independent from said back shaft when the releasable driveconnection of the back shaft is disengaged, and a'second prime moverenergizable for effecting a driving connection with the rotationalhousing of the lead differential when the selectively open and closedgear train is open, whereby respectively the selected relationshipof therotational rate *of'tlie' work'spindle to the tool feed rate ismaintained constant during disengagement of the first and second primemovers while maintaining a'driving connection between'the backshaft andthe lead differential and during maintenance of a colsed drive of thegear train connecting the rotatable housing of the lead differentialwith the lead screw as in performing a bobbing opera tion, and wherebythe selected relationship between the rotational rate of theworkspindle' to' the tool feed rate may be maintained as in threadmilling, a

WILLIAM W YER, JR, Primary Examiner; 7

1. A MACHINE TOOL SELECTIVELY CONVERTIBLE FOR USE AS A HOBBING MACHINEAND FOR THREAD MILLING COMPRISING A TOOL SPINDLE FOR RECEIVING ASELECTED CUTTER THEREON, A MAIN DRIVE SHAFT, A SINGLE DRIVE MEANS FORTHE SPINDLE AND DRIVE SHAFT, A ROTATABLE HOUSING LEAD DIFFERENTIALMECHANISM, A FIRST INDEX GEAR TRAIN, A WORK SPINDLE, A ROTATABLE HOUSINGTRAVERSE DIFFERENTIAL MECHANISM, A LEAD SCREW, SAID DRIVE SHAFT HAVING ARELEASABLE DRIVE CONNECTION WITH THE INPUT TO SAID LEAD DIFFERENTIAL, ASECOND INDEX GEAR TRAIN DRIVEN BY SAID SINGLE DRIVE AND HAVING A DRIVEINPUT TO THE TRAVERSE DIFFERENTIAL, SAID FIRST INDEX GEAR TRAINDELIVERING THE OUTPUT OF SAID LEAD DIFFERENTIAL TO THE WORK SPINDLE TOROTATE THE SAME AT A PRECISE ROTATIONAL RATE, SAID SECOND GEAR TRAINDETERMINING THE CUTTING GEAR RATE OF A TOOL ON THE TOOL SHAFT, MEANS FORDISENGAGING THE DRIVE SHAFT DRIVE TO THE WORK SPINDLE, A SELECTIVELYOPEN AND CLOSED GEAR TRAIN HAVING DRIVING CONNECTION ONLY, WHEN CLOSED,WITH SAID LEAD SCREW AND WITH THE ROTATIONAL HOUSING OF THE LEADDIFFERENTIAL MECHANISM, A PRIME MOVER ENERGIZABLE FOR EFFECTING APRECISE ROTATIONAL RATE TO THE WORK SPINDLE THROUGH SAID LEADDIFFERENTIAL AND INDEPENDENT FROM SAID DRIVE SHAFT WHEN THE RELEASABLEDRIVE CONNECTION OF THE DRIVE SHAFT IS DISENGAGEED, AND A SECOND PRIMEMOVER ENERGIZABLE FOR EFFECTING A DRIVING CONNECTION WITH THE ROTATIONALHOUSING OF THE LEAD DIFFERENTIAL WHEN THE SELECTIVELY OPEN AND CLOSEDGEAR TRAIN IS OPEN, WHEREBY RESPECTIVELY THE SELECTED RELATIONSHIP OFTHE ROTATIONAL RATE OF THE WORK SPINDLE TO THE TOOL FEED RATE ISMAINTAINED CONSTANT DURING DIS-ENGAGEMENT OF THE FIRST AND SECOND PRIMEMOVERS WHILE MAINTAINING A DRIVING CONNECTION BETWEEN THE DRIVE SHAFTAND THE LEAD DIFFERENTIAL AND DURING MAINTENANCE OF A CLOSED DRIVE OFTHE GEAR TRAIN CONNECTING THE ROTATABLE HOUSING OF THE LEAD DIFFERENTIALWITH THE LEAD SCREW AS IN PERFORMING A HOBBING OPERATION AND WHEREBY THESELECTED RELATIONSHIP BETWEEN THE ROTATIONAL RATE OF THE WORK SPINDLE TOTHE TOOL FEED RATE BE MAINTAINED AS IN THREAD MILLING.